I am not sure how much bitcoin you actually need to make it work, but I assume it is larger than the dust limit but still quite small. I would like more clarification here too.
Yes, the dust limit in Bitcoin is now lowered to 540 Satoshi (at Bitcoin v 0.9) from 5,400. In Coinprism it was rounded up to 600 Satoshis. This the amount used to send the transaction and carry your Colored Coins.
It doesn't matter if you send 1 or 10,000 colored coins, you are still technically sending 600 Satoshis to the recipient.